The goal of this proposal is to demonstrate that genetic deletion of PHLPP1 and PHLPP2, newly discovered phosphatases that selectively remove a phosphate from Ser473 on Akt, will modulate cardiac hypertrophy and survival through Akt dependent and independent mechanisms. Proposed work will examine the hypothesis that PHLPP1 and PHLPP2 have non-overlapping functions in cardiomyocytes and that global or cardiac- specific removal of distinct PHLPP isoforms will augment cardiac hypertrophy and failure. We have demonstrated for the first time that PHLPP1 and PHLPP2 are expressed in the heart and that decreasing PHLPP1 in cardiomyocytes or the heart increases Akt activity. The effect of PHLPP isoform removal in vitro and in vivo on cardiac signaling and development of hypertrophy following injury has not been investigated. Preliminary data suggests that removal of PHLPP2 in cardiomyocytes has no effect on Akt phosphorylation, however, increases cardiomyocyte size at baseline as well as following hypertrophic stimulation. To delineate the role of PHLPP1 and PHLPP2 in cardiomyocytes and the heart, the first aim will characterize the effect of PHLPP1 and PHLPP2 on cardiomyocyte signaling, hypertrophy and survival in vitro. Proposed experiments will use neonatal rat cardiomyocytes with gain and loss of PHLPP1 and PHLPP2 and adult cardiac myocytes from the PHLPP gene-target mice. The aim will investigate Akt as well as other signaling pathways that may be regulated by the PHLPP isoforms. This line of inquiry will be important for interpreting the cardiac phenotype of the PHLPP gene-targeted mice. The second aim will determine whether PHLPP1 and PHLPP2 gene-targeted mice show differences in the development of cardiac hypertrophy and failure in vivo. The cardiac phenotype of the PHLPP isoform gene-targeted mice will be examined at baseline and following pressure overload or agonist induced hypertrophy. The ability of the PHLPP isoforms to effect the transition from hypertrophy to failure will all be examined. Lastly, the third aim is to elucidate the mechanism of action of PHLPP1 isoforms in cardiomyocyte hypertrophy and in particular their ability to regulate phosphorylation and translocation of HDAC5 and GRK5. This proposal intends to discover new targets of PHLPP that may be helpful in providing innovative avenues for therapeutic strategies to treat heart disease.